Slashdot Mirror
Boeing's New 787 Wings — Amazingly Flexible
An anonymous reader writes "Boeing is making the wings of its new 787 out of carbon fiber instead of metal. That means the wings are so strong and flexible that they could bend upward and touch above the fuselage — or come close. The company is expected to deliver the first 787 to All Nippon Airlines in May 2008. 'Boeing has completed static testing of a three-quarter wingbox, but engineers are still considering whether to limit testing of the full wing to a 150% load limit held for 3 sec. or to continue bending it to see when it breaks. 'There's a raging debate within the engineering team to see if we should break it or not,' says [787 General Manager Mike] Bair.'" They have come a long way in wing flexibility.
I was wrong - 777. and the video is here - what a wonderful age we live in.
It's hard to believe that's how Micronians are made. Why don't we see it right now by having you both kiss one another?
It's potentially more dangerous than an alumnium wing, 150+% of design load has to be a substantial amount of energy stored in the wing, and while aluminum will deform in failure (converting most of the energy to heat) carbon fiber seems more likely to shatter.
Degaussing scares the bad magnetism out of the monitor and fills it with good karma.
You are joking, right? Assembly of the first A350 won't even begin for about 5 years. It's not at design freeze. The 787 is about to roll out, and first flight is in a few months.
Both companies have been using carbon fiber. The 787 uses an unprecedented amount of it. You can't say it's nothing new by citing an Airbus project that doesn't have a scheduled delivery until 2013. http://en.wikipedia.org/wiki/Airbus_A350
"They have come a long way from even just a year ago."
The linked video may have been uploded about a year ago, but it cites as its source a PBS production from 1995. (Which, incidentally, is discussing an entirely different airplane, the 777.)
With reasonable men I will reason; with humane men I will plead; but to tyrants I will give no quarter. -- William Lloyd
The point of the 787 is to fly further, more cheaply. So while costing less to fly, it is also supposed to do to the Pacific what the Boeing 767 did to the Atlantic market. That is, the 767 brought in a revolution of being able to connect mid-sized cities on both continents, rather than forcing people to go through hubs on larger aircraft such as the 747 or DC-10.
My doctorate is in Mechanical Engineering - Materials, in this case fracture mechanics. The fact that the wing is so strong suggests that it may be being over-designed. My graduate structures professor, who worked on the 747, point out that airplanes are designed for what might be called simultaneous mode failures -- there is no point in having the wings significantly stronger than the fuselage, as once the fuselage breaks the wings don't do you any good, you have just been carrying too much material in the wings. The same is true for all sub-systems. Hence, you have to do a very exhaustive analysis of the expected situations and make sure that all of them are appropriately covered, then you add a safety factor.
Typically, fatigue cracking has been the limiting factor in aircraft structures, and has caused numerous crashes. With the experience that has been gained in military programs, we should now know enough to use these composites properly.
You are joking, right? Assembly of the first A350 won't even begin for about 5 years. It's not at design freeze. The 787 is about to roll out, and first flight is in a few months.
Yeah, it kind of reminds me of when Airbus called Boeing's composite barrel design "old fashioned"!
Bearing in mind that nobody has produced such a design yet, including Airbus. Until Boeing did it a couple of weeks ago, that is.
The A350 was designed in direct response to the 787, which surprised Airbus in the amount of interest it received (they had at the time placed their bets on the now-troubled A380 program, which may never break even). Saying the 787 copied any of the A350's design or construction methods is getting it completely backwards.
The engineers at Boeing are smart enough to design the wing for optimal performance under normal conditions. That includes whatever wing bending occurs under nominal conditions.
If the aircraft is experiencing extreme conditions which are bending the wing excessively, then you _want_ to lose lift, rather than stress the wing and airframe more. Kind of like how sailors change to smaller sails during storms.
"National Security is the chief cause of national insecurity." - Celine's First Law
The fact that the 787 is a "plastic airplane" will get a lot of play, and having wings that bend, potentially to the point that they will tough, is just the most obvious and mediagenic manifestation of that. But it is just the tip of the iceberg of the innovations.
1) Yes, it's almost completely carbon fiber. This means that the plane can (and is) lighter, so it will be more fuel efficient. Also, it's easy to make complex curved shapes, so the wings and fuselage are slightly more aerodynamic. Because carbon fiber structures are so strong, the windows can be larger, and the plane can be pressurized to a lower altitude (it will be pressurized to 6000' instead of the typical 8000' of today's fleet). There is no corrosion, and little worry about fatigue in composites.
2) The plane is not built in Seattle, although that's where the final assembly takes place. All of the building takes place in multiple facilities around the globe, each producing parts to Boeing's plans. These parts will "snap together" in the Everett plant. The first 787 is being assembled right now, and will roll out on 7/8/7 (just over a week from now.) Apparently the left wing was off by 2 thousands of an inch or so, the right wing was absolutely perfect. Boeing converted three 747's to be gigantic cargo transporters to move all the parts from around the world to Everett.
3) The plane has almost completely electric, without the high-pressure pneumatic systems that older planes had. In particular, the AC systems are electric. This will be somewhat more efficient, and safer.
4) The plan for certification of the plane is borderline insane. The final assembly started a couple of weeks ago, and the plane will be rolled out in a week, the first flight will be in a couple of months, and the first delivery will be in Q2 2008. This is a tiny fraction of the time this process required on previous airplanes -- maybe 1/4 the time of the 777 and even less than that of the latest Airbus. This would be remarkable, even if the plane wasn't revolutionary in every other way, too!
5) Aviation Week and Space Technology visited the final assembly line recently, and were surprised to find that it was almost an empty building. That's not because they weren't ready -- that's because there are almost no tools needed to assemble the plane. They snap together the pieces, install the landing gear, and roll it down the building on its gear installing the various subassemblies. Boeing intends to assemble a plane every three days once they get going, a remarkable and unprecedented schedule.
Anyway -- there are so many revolutions in this airplane that I would have thought it was a scam if it was any other company than Boeing. It remains to be seen if they can meet their goals, but so far things are going remarkably according to the plan they laid out a few years ago.
Thad
I love Mondays. On a Monday, anything is possible.
Well Aircraft unlike computers are only operated by trained professionals.
Since you can not make the wing infinitely strong you you put operating limits in it.
One "neat" trick they use involves airspeed. When you start pulling Gs your stall speed goes up. Once a wing is stalled it stops generating lift so it unloads.
Back in the day your airspeed indicator had arcs. The green arc means that your wing will stall before it breaks.
The Yellow arc means that yes you can break the wing if you try.
The Red line means bad things are going to happen.
So when flying into storms the pilot can slow the the top of the green arc and be safe.
BTW a stall at altitude isn't a terrible thing. It is better than breaking the wing.
With this wing it may have an all Green arc.
As to breaking the structure to learn things. Yes but that kind of testing is expensive. If the wings of the 787 pass with a bigger than average margin then I would much rather see them do repetitive tests to see how it does with multiple over stress conditions.
The thing about some of the composites I have dealt with is some don't fail gracefully. I have parts of aircraft deform from stress but not totally fail. In other words it will get you home but she isn't going to fly again without A LOT of work.
I have seen carbon fiber get a good scratch in it and the next thing you know it is in a million part small parts.
See my blog http://ilovecookes.blogspot.com/ for light hearted technical information.
of course their is a downside to most changes.
by deform, you mean yield so, yes if you exceed the limit of carbon fibre you likely have snapped, where as aluminum, you have destroyed the structure of the frame. So if they both exceeded this limit at the same load, the aluminum may allow you to make it through one event.
For this to be obviously safer, you need:
1) the yield points would have to be very close.
2) it must be a single yield event (not repeated yield points, leading to a quick fatigue failure)
3) you must know the event occured so that you will replace the yieldied aluminium part, before the next event.
4) the yield event would still have to be in the yield strength of the aluminum, and not exceed it to the point of failure.
I think that is the issue, all of these are false. Carbon fibre has a much higher yield point, the aluminum wings constantly need inspected for fatigue cracks, and with each cycle they become closer to the point of failure.
With the carbon fibre, as the wing bends, it is probably designed to self limit the load. Since the aluminimum cannot survive the same amount of movement, it cannot self regulate (it bends, which makes it hot, which makes it softer, which makes it bend more which makes it hotter and softer,...)
of course it takes alott of energy to bend carbon fibre also, so it is releasing energy as heat as well. Granted aluminum is a much better heat conductor, so it would naturally transfer that heat better. But carbon fibre is known to stay stronger at high temperatures than aluminum.
Composites are significantly different from metal structures in that their primary failure modes are not fatigue related microfractures, but a phenomenon called delamination in which static and dynamic loading can cause the layers of alternating orientation fibers to separate. It could very well be that in order to design a wing that was not susceptible to delamination, the wing turned out to be incredibly flexible.
It sounds as if Boeing uses a "factor of safety" of 1.5, where the maximum anticipated load is multiplied by the factor of safety to determine the design strength of the wing. The factor of safety is calculated based on the earliest failure mode of the part, so it could simply be that other failure modes than wing deformation and buckling (as seen in the youtube video) are what determines the factor of safety with this new carbon fiber wing.
*most people never really think about the consequences*
Engineering ethics dictate that we take reasonable precautions to preserve human life, balancing extreme cases with the economic viability of producing the product in the first place.
l ight_587), where a possible gap in the maneuvering conditions / load conditions / stress analysis the FAA requires and airplane manufacturers design to led to an A300 jetliner to lose its tail in flight.
What reasonable is, depends on which field you look at. The same standards do not apply to structural engineering (buildings), civil engineering (bridges, dams), aerospace engineering (aircraft), electrical power engineering (building wiring, electrical distribution systems), etc etc.
The FAA standards are, they set a specific limit load condition calculation for classes of aircraft (light aircraft are different from jet transports carrying people, etc). That's based on performance, operational usage, and the number of people typically carried. There are load cases for limit loads for gust loading (suddenly hitting a headwind when you're already pulling Gs), wind shear, emergency pull-ups, etc. A speed is established, called maneuvering speed, below which nothing you can do to the aircraft is credibly likely to ever cause the aircraft to exceed the limit loads.
Then, you add a 50% safety factor on top of those loads (failure load >= 150% of design limit load), and demonstrate to the FAA's satisfaction that the aircraft meets that ultimate load. For jet transports carrying people, the demonstration requires that you take it out to the 150% load limit and see if it breaks there.
Now, that ultimate load can be expected to cause permanent damage to the wings. Pretty much any aircraft exceeding the design limit load (100%) will get grounded, and anything approaching 150% is guaranteed to have damage. Since the test to 150% damages the test structure for any aluminum aircraft, the usual assumption is that it's a good idea to just keep testing past 150% until it breaks.
But you just need to prove that it meets the 150% for the FAA to be happy.
Designers try to make the failure point slightly, but not too much, past 150% of design limit load. Because adding weight is expensive (operations costs), and as others have mentioned it doesn't do any good for the wing to be stronger if the fuselage breaks first, etc. The loads are all balanced; it's inefficient for things to fail at different points.
These standards are reasonable, for transport aircraft. We know that because large jets are not falling out of the sky due to wing failures. I can't offhand think of the last one that wasn't due to some external cause (collision, etc). There closest incident recently was the American Airlines 587 crash in 2001 (http://en.wikipedia.org/wiki/American_Airlines_F
In a previous life, I did a lot of work on major structural repairs to composite fibre airframe structures - and more specifically on sailplanes. I had several qualifications for inspection and maintenance on them, and worked in a shop that did everything up to and including spar repairs. There's actually less requirements for inspections on any form of composite structure than metal or wooden frame. And when there was inspections, it was much simpler. For example, the spar is tested simply by taking two identical tuning forks, placing one on one end of the spar, ringing the second one, placing it on the other end of the spar. If the other one rang in sympathy, things were fine. The wing surface itself is very easily checked for delamination by simply tapping and listening. When you're more experienced, you can feel it in the way your tapping object responds to the impact. That's far easier that some of the x-ray type inspections we had to do on the metal aircraft. That sort of level of inspection was only done once a year, or every 200 hours, whichever came first. Given the rest of the aircraft industry inspection schedules, I highly doubt that anything will change for the 787.
You are correct that microfine stress fractures are impossible to see in a pure carbon structure. To work around that, every object has a very fine fibreglass layer (070 or thinner) on the outside surface. When stress is applied, the fibreglass shows the stress marks and you can then visually see that something is wrong.
The biggest issue with C/f structures is design life. At the time when I was last working in the industry (mid 90's), they weren't even sure what the maximum life was. There was no data anywhere in the world. The sailplane factories were stating that 10K hours was the minimum and they would test after that (metal airframes were 30K hours before EoL). There were studies being done at Melbourne's RMIT (Australia). The last I heard there was they got to 17K hours before failure of one wing. Given the absurd number of hours a commercial airliner does compared to a sailplane, I would hope and expect that they have done some lifetime studies beyond that. I haven't yet seen any numbers from Boeing about expected airframe life for their pure composite structures.
Life is complete only for brief intervals in between toys or projects -- John Dalton